Study of microstructure and mechanical properties of narrow-gap multi-layer hybrid laser-arc welded 316L austenitic stainless steel

Hybrid laser-arc welding is an emerging welding technology that has a promising prospect in large-scale equipment manufacturing. In this paper, the butt joint of 316L austenitic stainless steel with 40 mm was made by using the multi-layer hybrid laser-arc welding process. On this basis, microstructure and properties of the welded joint were further investigated using an optical microscope, scanning electron microscope, and other methodologies. The results showed that the base materials consist of massive polygonal austenitic with a small amount of ferrites distributed in the grain boundary. What is more, the 316L austenitic stainless steel was heated and solidified in an F-A mode. Thus, ferrites distributed in the grain boundary were coarsened in the heat affected zone and the fusion zone was also composed of massive austenite and ferrites, which were approximately perpendicular to the fusion line. Owing to the different thermal cycles of different layers, the microstructure of the upper layer was coarser than that of the lower layer, and this microstructural inhomogeneity led to the variation of the hardness within the welded joint: hardness value of the upper weld was slightly higher than that of the lower weld. In addition, all tensile specimens were failed at the fusion zone and showed an obvious characteristic of ductile fracture with massive dimples distributing on it. Consequently, this study will broaden the scope of the application for the thick-plate hybrid laser-arc welding technology.